Timing and Nature of Wet Climatic Periods in North Africa and in the Arabian Peninsula: Inferences from Isotopic, Chronologic, and Remote sensing data
Thursday, 17 December 2015
Poster Hall (Moscone South)
The wet climatic periods in the Quaternary in north Africa and in Arabia were traditionally attributed to intensification of paleo-monsoons during interglacial periods and progressive northward migration of monsoonal front. In N Africa, the monsoonal model could not account for: (1) progressive W to E depletion (Morocco: -20 to -40‰; ; Libya: -70 to -80‰; Egypt: -80 to -83‰) in isotopic composition of fossil groundwater ; (2) observed high lake levels during glacial periods (e.g., Lake Lisan: 160 m bmsl during glacial period MIS2); (3) the depleted isotopic compositions in the groundwater compared to modern precipitation (e.g., d2H: Morocco: - 25.8‰; ; Libya: -17.7; Egypt: -11.7‰) is consistent with deposition during relatively cool periods; (4) ages (Cl-36 : 170ka to 1000ka) of groundwater in the Empty Quarter are consistent with deposition in glacial periods; and (5) low recharge temperatures (e.g., 2-6 °C below average annual temperatures). Intensification of the paleo-westerlies during previous glacial periods can account for these observations. We propose a similar model for northern and central Arabia and probably the northern sectors of the Empty Quarter. Our reasoning: (1) a progressive north to south depletion in groundwater composition (north & center: d2H :-26.6 to -2.5‰, south: d2H: -76.6 to -26.9‰) is inconsistent with a paleo-monsoon origin; (2) ages of sediments in paleo-lakes (e.g., lake Mundafan: OSL ages: 88 to 147ka) favor deposition during glacial periods; (3) depleted isotopic compositions in the groundwater (d2H: -76.6 to -26.9‰) compared to modern precipitation (d2H: -22 to -45‰); (4) Cl-36 ages of groundwater (170ka to 1000ka ) are consistent with precipitation during glacial periods; (5) well documented records of monsoon-related wet events in Oman are not well developed northwards; and (6) well developed paleo-channels and theater-headed valleys in north and central Arabia compared to southern Arabia.